Well, after thinking about it, there are a few inbalanced things that could be changed.
Weather: Oh boy, BW OU, the big weather battle field. I still think weather is a big problem, especially since weather is permanent in this generation. This can cause some extra, unnecessary damage from Sand, and with Swift Swim Pokemon all over the place, huge threats like Kingdra emerge. Of course, you also have the Sand Rush abusers as well. Sun also exists, giving Venusaur the ability to heal 66% of it's health, which can lead to some nasty stalling. While Hail is not common at all, it's still worth mentioning the damage that it can give, like Sand. With Toxicroak being some what popular, it gets harmed by the Sun as well. Also note that Tyranitar and other Rock-types get the 50% SpDef boosts in the Sand as well, ruining some calculations. What are the ways to fix this you ask? Well, we could start by doing one of three things: Ban weather activating abilities, ban the weather abusers (Excadrill, Kingdra), or we could ban the weather abuser's abusing abilities (Sand Rush, Swift Swim). However, those things will most likely not happen. But who knows what the future holds? Perhaps a Politoed suspect could emerge... But that's probably not happening either haha.
Jirachi: Yes, the Scarf set specifically wants to make me delete this Pokemon from the existence of generation 5. While I love Jirachi as a Pokemon, I think it needs to be bumped up from OU. It's Scarf set can lead to some nasty hax, which ruins games for a lot of players. I can say this from experience as well, as I love to use Scarf Jirachi. Not only this, but out speeding everything is great too. While that might sound obvious, having access to U-Turn allows it to pivot out with ease. Not only that, but it can use that Healing Wish, and recover a Pokemon to full health and removing all status. It also has great typing, only sharing it with Metagross. With it's great move pool, it could also run a cancerous paraflinch set, being able to hax anyone out, one of the main problems the Pokemon causes. With it's 100-across-the-board stats, it can run not only a physical set, bet a special one too, with moves like Ancient Power, Psychic, Thunderbolt, and many more. It's capabilities are endless, because it even has access to moves like Substitute and Wish. Those are a few reasons why I think it's a problem in the meta game, however I'm not really warranting a ban or suspect.
Those are some things that I think are issues in the meta game right now, I know there are more things I can't think of right now and I'll add them later.